In a known vehicle power seat, various driving force transmitting devices are proposed which transmit a rotation torque of a drive shaft rotated by a driving source, such as a motor, to a driven shaft having an axis extending in a direction different from a direction of an axis of the drive shaft. In these devices, the rotation torque is transmitted by engaging a worm gear of the drive shaft with a helical gear of the driven shaft. The worm gear and the helical gear are rotatably accommodated in a supporting member (gear housing). One of such driving force transmitting devices is shown in a patent document 1, in which the driving force transmitting device for transmitting the rotation torque of the drive shaft to a screw shaft, includes a worm gear provided at the drive shaft, a helical gear provided at the screw shaft, and a gear case (a portion of a gear housing) having a pair of first bearing wall portions, a pair of second bearing wall portions formed integrally with the pair of first bearing wall portions and an opening at one side for accommodating the worm gear and the helical gear from the opening. The first bearing wall portions are provided opposite to the axial line direction of the drive shaft and rotatably supporting the both end portions of the worm gear and the second bearing wall portions are provided opposite to an axis direction of the screw shaft and rotatably supporting the both end portions of the helical gear. According to the patent document 1, since the pair of first bearing wall portions rotatably supporting the both end portions of the worm gear and the pair of second bearing wall portions rotatably supporting the both end portions of the helical gear are integrally formed, accurate positioning of each gear relative to each shaft can be easily achieved. Further, one gear engaging with the other gear being assembled bisecting with right angles, can be easily inserted into the opening provided at one side for easy assembling of the gears into the hear case.
Patent Document 1: WO2008/087947A1
However, according to the driving force transmitting device of the patent document 1, a motor as a drive force source for the power seat and a speed reduction portion with direction changing gear mechanism are structured as a unit and supported by a bracket. The screw shaft is set to the speed reduction portion with the rail as a unit to which the speed reduction portion with direction changing gear mechanism has been pre-assembled. Upon assembling, a pair of tip ends of the screw shaft at the paired rail side are respectively inserted into the speed reduction portion with direction changing gear mechanism (edge of the helical gear in the gear case) supported at both sides of the bracket and the speed reduction portion with direction changing gear mechanism is fixed to the attaching bracket from the upper rail side by fastening bolt. Therefore, if the screw shaft side inserting position (rotation phase) at the rail side is deviated from the speed reduction portion (helical gear edge) side inserting position (rotation phase), the screw shaft, which, has been preset to the rail side, is rotated for adjusting the relative rotational position to agree with the position of the helical gear edge. However, since the screw shaft is of an elongated lengthy shape, it is difficult to manually rotate the screw shaft and therefore, the assembling becomes a troublesome work. Further, the pair of right and left side screw shafts, to which the pair of rails is pre-assembled, has to be assembled to the speed reduction portion with direction changing gear mechanism at both sides. If the inserting position of the speed reduction portion side (helical gear edge) is deviated from the corresponding position to be inserted in right/left direction, the assembling work becomes further difficult. Also, if the pitch of pair of rails to be secured to the vehicle floor is deviated from each other, assembling of the driving force transmitting device becomes difficult.
A need thus exists for a driving force transmitting device and a vehicle seat slide device which is not susceptible to the drawback mentioned above.